1. Field of the Invention
This invention relates to a flame-retardant rubber-modified styrene resin composition, and more particularly to a flame-retardant rubber-modified styrene resin composition which has excellent light resistance, heat resistance moldability, and impact resistance.
2. Description of the Background
Rubber modified styrene resins, represented by impact-resistant polystyrene and ABS resin, have excellent mechanical characteristics and a good electric insulating ability, and are processed or molded with ease to give articles with good outward appearances. Because of this, the rubber-modified styrene resins are widely used for a variety of industrial articles, including automobile parts, electric appliances, construction materials, and the like.
The rubber-modified styrene resins, however, are limited with respect to their field of application because of their ready flammability Specifically, various rules and regulations have been promulgated in recent years controlling the use of flammable materials in view of safety. These rules and regulations restrict the field of application of the rubber-modified styrene resins.
In addition to flame retardancy, a heat resistance of a degree which prevents the formed material from deforming at a relatively high temperature of use is required for the rubber-modified styrene resins used in some parts of business machines such as office automation business machines. Moreover, a problem in these resins recently drawing special attention is discoloration of the outer surface of the material by direct sun-light or light from a fluorescent lamp when these resins are used for sheathing the outer surfaces of machines. Good light resistance therefore is an essential property for these resins.
Accordingly, many functional properties, including not only flame retardancy but also heat resistance and light resistance, are required for the flame-retardant rubber-modified styrene resins.
For these reasons, an attempt has been made to compound a flame retardant material with a high boiling point such as, for example, a halogenated diphenylether, with the rubber-modified styrene resins to make them flame-retardant. However, the use of such a flame retardant agent causes a decline in the light resistance of the resins, although it can improve the flame retardancy and heat resistance.
When a halogenated bisphenol type polycarbonate oligomer is compounded with the resin as a flame retardant agent, it can improve the heat resistance and light resistance, but impairs the fluidity. In addition, this impact-resistant property due to improper dispersion in the resin to which it has been compounded. For these reasons resins with which such a flame retardant agent has been compounded have not been accepted as an industrially practical material.
As another attempt, a composition was proposed wherein a halogenated bisphenol type polycarbonate oligomer and a tetrahalogenated bisphenol type compound are compounded in a specific proportion (Japanese Patent Publication No. 54347/1985). However, the purpose of compounding a tetrahalogenated bisphenol type compound with rubber-modified styrene resins is directed to prevention of blooming effects and improvement of heat resistance, and cannot provide a composition with a high light resistance and heat resistance, nor one with a practical moldability and impact resistance. This composition therefore is not a satisfactory material for meeting a high degree of requirements.
In view of this situation, the present inventors have conducted extensive studies for preparing a flame-retardant rubber-modified styrene resin composition possessing excellent light resistance and heat resistance, as well as practical moldability and impact resistance. As a result, the inventors have found that these objects could be accomplished by compounding with such resins a halogenated polyolefin component at a specific proportion, in addition to a mixture of a halogenated bisphenol type polycarbonate oligomer and a tetrahalogenated bisphenol type compound at a certain ratio. The finding has led to the completion of this invention.